But yes, you're right in that the gaseous propane fuel is a restriction, in theory, however I have never seen any documentation to find out if this is an actual real-world factor. You can also get gaseous propane injectors that inject the propane gas right at the cylinder ports. Sort of a compromise between the old mixer and the liquid system, with the drawbacks of both.
If you're not racing, propane is an excellent fuel for spark-ignition engines. Besides having excellent fuel distribution, its gaseous nature ensures that engines last longer because it doesn't wash oil off from cylinder walls.
While gaseous fuels produce less full throttle power because they reduce the engine's volumetric efficiency, the fact that they also reduce volumetric efficiency at part throttle means that the throttle must be opened slightly more, which reduces manifold vacuum. Propane gets a slight fuel efficiency boost by the slight reduction in pumping losses with lower manifold vacuum.
One issue with liquid injection is that the fuel is continuously circulated back to the fuel tank. The fuel then picks up heat from the pump, from the engine, and from radiation from hot pavement. If the fuel pump fails, then you need to empty the fuel tank (like an AC system) to fix it. Without a fuel pump, fuel will flow to a propane carburetor down to -40°F. Both vapour and liquid injection systems both need some additional tank pressure (ie, from ambient temperature) in order to run.
Propane carburetors also don't need a choke to start in cold weather and will idle smoothly immediately after starting. This is video of my Pontiac starting at 0°F:
[video:youtube]
https://youtu.be/74CqA71DmRA[/video]
A drawback for some is an advantage for others.
